ask your ex-employer about how the 401k will be handled. As for other items since the paycheck and repayment were in the same year the IRS dictates that your W-2 should only reflect the correct (net) amounts. example if including the April paycheck your federal withholding was $6500 and that April paycheck which you repaid showed $1000 in federal withholding your 2024 w-2 should show only $5500 in federal withholding. So there really is nothing extra you have to do when doing your 2024 return.
